1. Field of the Invention
The present invention relates to techniques for synchronizing devices in a network. More specifically, the present invention relates to an in-band synchronization technique for devices.
2. Related Art
It is often necessary to synchronize devices in a communication system that utilizes a time-domain multiple-access (TDMA) communication protocol. This synchronization ensures that all of the devices start their time slots at approximately the same time so that all of the time-slot boundaries are aligned. For example, in a communication system that has 1-ms time slots, the synchronization may be accurate to within 10-20 μs.
In some communication systems, this synchronization is achieved using devices that have highly stable and accurate clock circuits, which are synchronized once (for example, when they are manufactured). However, providing these clock circuits increases the cost of the devices, and thus, the overall cost of the communication system.
Alternatively, in many distributed communication systems, less-expensive clock circuits are synchronized using an external reference signal, such as the signals provided by the global positioning system (GPS). While this synchronization technique is often suitable in outdoor communication systems, it may not work in indoor communication systems or in vehicle applications where a vehicle may go in and out of GPS reception.
Moreover, in these communication systems the external reference signal is typically provided by a central authority (such as the GPS) that organizes or manages the synchronization of the devices. Unfortunately, in many communication systems, such as ad hoc networks, this type of central authority is not available. This makes the use of less-expensive clock circuits more difficult, and may also result in less efficient use of the available communication bandwidth (e.g., larger guard bands may be needed between adjacent time slots).
Hence, what is needed is a method and an apparatus that facilitates synchronization in communication systems without the problems listed above.